从Rust中的数组调用闭包 [英] Calling closures from an array in Rust

问题描述

如何迭代闭包的数组，依次调用每个闭包？

How do I iterate over an array of closures, calling each one in turn?

对于函数，我发现我可以通过迭代数组来做到这一点，并取消引用产生的值：

With functions, I discovered I could do this by just iterating over the array, and dereferencing the values that produced:

fn square(x: int) -> int { x * x }

fn add_one(x: int) -> int { x + 1 }

fn main() {
    let funcs  = [square, add_one];
    for func in funcs.iter() {
        println!("{}", (*func)(5i));
    }
}

然而，当我尝试对closures ，我得到一个错误：

However, when I try to do the same with closures, I get an error:

fn main() {
    let closures = [|x: int| x * x, |x| x + 1];
    for closure in closures.iter() {
        println!("{}", (*closure)(10i));
    }
}

产生：

<anon>:4:24: 4:34 error: closure invocation in a `&` reference
<anon>:4         println!("{}", (*closure)(10i));
                                ^~~~~~~~~~
note: in expansion of format_args!
<std macros>:2:23: 2:77 note: expansion site
<std macros>:1:1: 3:2 note: in expansion of println!
<anon>:4:9: 4:41 note: expansion site
<anon>:4:24: 4:34 note: closures behind references must be called via `&mut`
<anon>:4         println!("{}", (*closure)(10i));
                                ^~~~~~~~~~
note: in expansion of format_args!
<std macros>:2:23: 2:77 note: expansion site
<std macros>:1:1: 3:2 note: in expansion of println!
<anon>:4:9: 4:41 note: expansion site

我尝试声明迭代变量 ref mut ，它仍然不起作用：

If I try declaring the iteration variable ref mut, it still doesn't work:

fn main() {
    let closures = [|x: int| x * x, |x| x + 1];
    for ref mut closure in closures.iter() {
        println!("{}", (*closure)(10i));
    }
}

结果：

<anon>:4:24: 4:39 error: expected function, found `&|int| -> int`
<anon>:4         println!("{}", (*closure)(10i));
                                ^~~~~~~~~~~~~~~
note: in expansion of format_args!
<std macros>:2:23: 2:77 note: expansion site
<std macros>:1:1: 3:2 note: in expansion of println!
<anon>:4:9: 4:41 note: expansion site

我添加另一个引用：

fn main() {
    let closures = [|x: int| x * x, |x| x + 1];
    for ref mut closure in closures.iter() {
        println!("{}", (**closure)(10i));
    }
}

我回到原来的错误：

<anon>:4:24: 4:35 error: closure invocation in a `&` reference
<anon>:4         println!("{}", (**closure)(10i));
                                ^~~~~~~~~~~
note: in expansion of format_args!
<std macros>:2:23: 2:77 note: expansion site
<std macros>:1:1: 3:2 note: in expansion of println!
<anon>:4:9: 4:42 note: expansion site
<anon>:4:24: 4:35 note: closures behind references must be called via `&mut`
<anon>:4         println!("{}", (**closure)(10i));
                                ^~~~~~~~~~~
note: in expansion of format_args!
<std macros>:2:23: 2:77 note: expansion site
<std macros>:1:1: 3:2 note: in expansion of println!
<anon>:4:9: 4:42 note: expansion site

我在这里缺席吗？

推荐答案

.iter（）方法的向量产生不可变的引用，你需要可变的调用闭包，因此你应该使用 .iter_mut（）：

The .iter() method of vector yields immutable references, you need mutable ones to call the closure, thus you should use .iter_mut() :

fn main() {
    let mut closures = [|x: int| x * x, |x| x + 1];
    for closure in closures.iter_mut() {
        println!("{}", (*closure)(10i));
    }
}

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